Asphalt finisher

Abstract

The present invention provides a technology that is able to inhibit occurrence of damage in a roadbed during construction of asphalt pavement thereon. An asphalt finisher 100 comprises: a tractor 1; a hopper 2 that is installed on the front side of the tractor 1 and that accepts paving material; a conveyor CV that feeds the paving material inside the hopper 2 to the rear side of the tractor 1; a screw SC that spreads out the paving material, which has been fed by the conveyor CV, on the rear side of the tractor 1; a screed 3 that levels the paving material, which has been spread out by the screw SC, on the rear side of the screw SC; and a controller 50 (front-wheel drive force control unit 50B) that controls, on the basis of the weight of the paving material inside the hopper 2, the drive force of front wheels 6 of the tractor 1.

Description

[Technical field]

[0001] The present disclosure relates to an asphalt finisher. [Background technology]

[0002] An asphalt finisher is known that includes a tractor, a hopper, a conveyor that transports the paving material in the hopper to the rear of the tractor, a screw that spreads the paving material transported by the conveyor, and a screed that spreads the paving material behind the screw (see Patent Document 1).

[0003] The asphalt finisher constructs asphalt paving while receiving paving material from the loading platform of the dump truck adjacent to the front of the vehicle into a hopper. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-63650 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the amount of paving material in the hopper is relatively large when the dump truck starts to load it, but gradually decreases as construction progresses. Therefore, as the amount of paving material in the hopper located at the front of the tractor decreases, the load on the front wheels of the tractor decreases, and as a result, the frictional force between the front wheels and the ground (roadbed) becomes relatively small, so that the driving force of the front wheels may become greater than the frictional force. Therefore, if the front wheels slip, the roadbed may be dug up and damaged.

[0006] Therefore, an object of the present invention is to provide a technology capable of suppressing damage to the roadbed during construction of asphalt pavement. [Means for solving the problem]

[0007] In order to achieve the above object, in one embodiment of the present disclosure, A tractor, A hopper installed in front of the tractor to receive paving materials; a conveyor that conveys the paving material in the hopper to the rear side of the tractor; A screw that spreads the paving material transported by the conveyor behind the tractor; A screed that spreads the paving material spread by the screw on the rear side of the screw; a control unit that controls a driving force of a front wheel of the tractor based on a weight of the paving material in the hopper; An estimation unit that estimates the weight; A spatial recognition device that acquires data for monitoring the condition of the paving material in the hopper; Equipped with 、 The estimation unit estimates the weight based on an output of the spatial recognition device, The control unit controls a driving force of a front wheel of the tractor based on a result of the weight estimation by the estimation unit. R, An asphalt finisher is provided. Effect of the Invention

[0008] According to the above-described embodiment, damage to the roadbed during construction of the asphalt pavement can be suppressed. [Brief description of the drawings]

[0009] [Figure 1A] FIG. 1 is a schematic diagram of an asphalt finisher. [Figure 1B] FIG. 1 is a schematic diagram of an asphalt finisher. [Diagram 2] FIG. 2 is a functional block diagram showing an example of a configuration of a controller. [Diagram 3] FIG. 2 is a hydraulic circuit diagram showing an example of the configuration of a hydraulic system of an asphalt finisher. [Figure 4] 11A and 11B are diagrams illustrating an example of a method for controlling the driving force of the front wheels. [Figure 5A] FIG. 2 is a front view showing the state of the paving material inside the hopper. [Figure 5B] FIG. 2 is a front view showing the state of the paving material inside the hopper. [Figure 5C] FIG. 2 is a front view showing the state of the paving material inside the hopper. [Figure 5D] FIG. 2 is a front view showing the state of the paving material inside the hopper. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment will be described with reference to the drawings.

[0011] [Overall configuration] First, with reference to FIG. 1, the overall configuration of an asphalt finisher 100 according to this embodiment will be described.

[0012] 1A and 1B are diagrams showing an example of an asphalt finisher 100 according to this embodiment. Specifically, Fig. 1A is a left side view of the asphalt finisher 100, and Fig. 1B is a top view of the asphalt finisher 100.

[0013] 1, the asphalt finisher 100 is disposed so that its vehicle length direction, vehicle width direction, and vehicle height direction correspond to the X-axis direction, Y-axis direction, and Z-axis direction, respectively. Specifically, the front side of the vehicle length direction, i.e., the front direction of the asphalt finisher 100, corresponds to the X-axis positive direction (+X side), and the rear side of the vehicle length direction, i.e., the rear direction of the asphalt finisher 100, corresponds to the X-axis negative direction (-X side). In addition, the left side of the vehicle width direction, i.e., the left direction of the asphalt finisher 100, corresponds to the Y-axis positive direction (+Y side), and the right side of the vehicle width direction, i.e., the right direction of the asphalt finisher 100, corresponds to the Y-axis negative direction (-Y side). In addition, the upper side in the vehicle height direction, i.e., the upward direction of the asphalt finisher 100, corresponds to the positive direction of the Z axis (+Z side), and the lower side in the vehicle height direction, i.e., the downward direction of the asphalt finisher 100, corresponds to the negative direction of the Z axis (-Z side).

[0014] As shown in FIGS. 1A and 1B, the asphalt finisher 100 includes a tractor 1, a hopper 2, a conveyor CV, a screw SC, and a screed 3.

[0015] The tractor 1 corresponds to the main body of the asphalt finisher 100, and drives the asphalt finisher 100. The tractor 1 includes rear wheels 5 and front wheels 6, and drives the asphalt finisher 100 by rotating the rear wheels 5 using a rear-wheel drive motor 20 (see FIG. 3) and rotating the front wheels 6 using a front-wheel drive motor 22 (see FIG. 3).

[0016] The tractor 1 may be equipped with crawlers instead of the wheels (rear wheels 5 and front wheels 6).

[0017] 1A, a driver's seat is provided on the upper part of the tractor 1. An operator can operate the asphalt finisher from the driver's seat on the upper part of the tractor 1.

[0018] As shown in FIGS. 1A and 1B, the tractor 1 is equipped with a controller 50, for example.

[0019] The controller 50 controls the asphalt finisher 100 .

[0020] The functions of the controller 50 may be realized by any hardware or any combination of hardware and software. The controller 50 is mainly composed of a computer including, for example, a central processing unit (CPU), a memory device such as a random access memory (RAM), a non-volatile auxiliary storage device such as a read only memory (ROM), and an interface device for input and output with the outside. The controller 50 realizes various functions by, for example, loading a program installed in the auxiliary storage device into the memory device and having the CPU execute the program.

[0021] For example, the controller 50 may control the discharge amount of various hydraulic pumps (to be described later) that supply hydraulic oil for driving hydraulic actuators. The hydraulic actuators include various hydraulic cylinders and hydraulic motors (to be described later).

[0022] Also, for example, the controller 50 may control the flow of hydraulic fluid between a hydraulic actuator and a hydraulic pump.

[0023] The hopper 2 receives the paving material supplied from the bed of a dump truck. The paving material is, for example, an asphalt mixture.

[0024] As shown in FIG. 1A and FIG. 1B, the hopper 2 is provided at the front of the tractor 1. As described later, the hopper 2 includes left and right hopper wings 2W (left hopper wing 2WL and right hopper wing 2WR) (see FIG. 5), and is configured so that the left and right hopper wings 2W can be opened and closed in the Y-axis direction (vehicle width direction) by the hopper cylinder 24. The asphalt finisher 100 usually receives paving material from the bed of the dump truck with the hopper 2 fully open. Even when receiving paving material from the bed of the dump truck, the asphalt finisher 100 continues traveling while pushing the dump truck forward via the push roller 2b. When the paving material in the hopper 2 decreases, the operator of the asphalt finisher 100 closes the hopper 2, and the paving material near the inner wall of the hopper 2 is collected in the center of the hopper 2. As a result, even when there is a relatively small amount of paving material inside the hopper 2, the asphalt finisher 100 can maintain a state in which the conveyor CV at the bottom of the center of the hopper 2 can transport the paving material to the rear of the tractor 1. The paving material transported to the rear of the tractor 1 is spread by the screw SC in the vehicle width direction in the area toward the tractor 1 and in front of the screed 3.

[0025] Incidentally, FIG. 1 shows the asphalt finisher 100 when the hopper 2 is in a fully open state.

[0026] In addition, the tractor 1 is equipped with a spatial recognition device CM.

[0027] The spatial recognition device CM is attached to the front upper surface of the tractor 1, specifically, to the front end of the driver's seat at the top of the tractor 1, and acquires data for monitoring the state of the paving material in the hopper 2. The spatial recognition device CM may include, for example, an imaging device capable of imaging the inside of the hopper 2. The imaging device may include, for example, a monocular camera, a stereo camera, a three-dimensional camera, a depth camera, or the like. The spatial recognition device CM may also include a distance sensor, for example, a LIDAR (Light Detecting and Ranging), a millimeter wave radar, an ultrasonic sensor, or the like. The output data of the spatial recognition device CM is input to the controller 50. As a result, the controller 50 can recognize the amount of paving material in the hopper 2 based on the output data of the spatial recognition device CM.

[0028] The conveyor CV transports the paving material in the center of the hopper 2 to the rear side of the tractor 1. The conveyor CV is driven by a hydraulic motor (a conveyor motor 21C described later) that rotates by receiving hydraulic oil from a hydraulic pump (a conveyor screw pump 14S described later). Specifically, the conveyor CV is configured to transport the paving material in the hopper 2 to the rear side of the tractor 1 through a transport passage CP provided in the tractor 1. The transport passage CP is a substantially rectangular parallelepiped space formed inside the tractor 1, and has a substantially rectangular entrance OP that opens into the hopper 2 on the front side of the tractor 1. The conveyor CV includes, for example, two conveyors that are arranged on the left and right sides of the center of the vehicle width direction (Y-axis direction) of the asphalt finisher 100 (tractor 1). Of the two conveyors, the left conveyor is configured to transport the paving material toward the left main screw SCLM described later, and the right conveyor is configured to transport the paving material toward the right main screw SCRM described later.

[0029] As described above, the screw SC spreads the paving material transported by the conveyor CV onto the ground behind the tractor 1. The screw SC is driven by a hydraulic motor (a screw motor 21S described below) that rotates by receiving hydraulic oil from a hydraulic pump (a conveyor / screw pump 14S described below). The screw SC includes a left main screw SCLM, a right main screw SCRM, a left extension screw SCLE, and a right extension screw SCRE.

[0030] The left main screw SCLM and the right main screw SCRM are disposed so as to be contained within the width of the tractor 1 in the vehicle width direction. The left extension screw SCLE is connected to the left end of the left main screw SCLM, and disposed so as to protrude leftward from the left end of the tractor 1 in the vehicle width direction (Y-axis direction). The right extension screw SCRE is connected to the right end of the right main screw SCRM, and disposed so as to protrude rightward from the right end of the tractor 1 in the vehicle width direction.

[0031] The screed 3 spreads the spread paving material behind the screw SC. The screed 3 includes a main screed 30 and an extendable screed 31.

[0032] The main screed 30 includes, for example, a left main screed and a right main screed that are arranged on the left and right sides of the center of the vehicle width direction of the asphalt finisher 100 (tractor 1). The telescopic screed 31 includes a left telescopic screed 31L and a right telescopic screed 31R. The main screed 30, the left telescopic screed 31L, and the right telescopic screed 31R are arranged shifted forward and backward so as not to overlap in the vehicle length direction (X-axis direction). Specifically, in the vehicle length direction, the left telescopic screed 31L is arranged behind the main screed 30, and the right telescopic screed 31R is arranged behind the left telescopic screed 31L.

[0033] The telescopic screed 31 is configured to be extended and retracted in the vehicle width direction by the screed telescopic cylinder 27. The screed telescopic cylinder 27 is supported by a support part fixed to the rear surface of the housing of the main screed 30, and is configured to be able to extend and retract the telescopic screed 31 in the vehicle width direction. The screed telescopic cylinder 27 includes a left screed telescopic cylinder 27L and a right screed telescopic cylinder 27R. The left screed telescopic cylinder 27L can extend and retract the left telescopic screed 31L to the left in the vehicle width direction relative to the main screed 30. The right screed telescopic cylinder 27R can extend and retract the right telescopic screed 31R to the right in the vehicle width direction relative to the main screed 30.

[0034] The screed 3 is a floating screed towed by the tractor 1 and is connected to the tractor 1 via levelling arms 3A. The screed 3 is moved up and down together with the levelling arms 3A by the extension and retraction of the screed lift cylinders 25.

[0035] The leveling arm 3A is configured to be able to connect the screed 3 to the tractor 1. Specifically, one end of the leveling arm 3A is connected to the screed 3, and the other end is rotatably connected to the tractor 1. The leveling arm 3A includes a left leveling arm 3AL and a right leveling arm 3AR.

[0036] The leveling cylinder 23 is configured to be able to move the front end portion of the leveling arm 3A up and down in order to adjust the spreading thickness (paving thickness) of the paving material. Specifically, as shown in Fig. 1A, the leveling cylinder 23 may have a cylinder portion connected to the tractor 1 and a rod portion connected to the front end portion of the leveling arm 3A.

[0037] The front end portion of the leveling arm 3A is slidably supported by the tractor 1. When increasing the paving thickness, the controller 50 causes the hydraulic oil discharged by the hydraulic pump (cylinder pump 14M described below) to flow into the rod side oil chamber of the leveling cylinder 23, contracting the leveling cylinder 23 to raise the front end portion of the leveling arm 3A. On the other hand, when decreasing the paving thickness, the controller 50 causes the hydraulic oil in the rod side oil chamber of the leveling cylinder 23 to flow out, and extends the leveling cylinder 23 to lower the front end portion of the leveling arm 3A.

[0038] The screed lift cylinder 25 is used to lift the screed 3 from a construction state (hereinafter, "construction state") to a state (hereinafter, "lifted-up state") relatively away from the ground, and to return the screed 3 from the lifted-up state to the construction state. In this way, in situations other than asphalt pavement construction work, the screed 3 is maintained in a lifted-up state relatively away from the ground (roadbed), and the screed 3 or roadbed can be prevented from being damaged by contact between the screed 3 and the ground. Specifically, as shown in FIG. 1A, the screed lift cylinder 25 may have a cylinder portion connected to the tractor 1 and a rod portion connected to the rear end portion of the leveling arm 3A. When lifting the screed 3, the controller 50 causes hydraulic oil discharged by a hydraulic pump (cylinder pump 14M described later) to flow into the rod-side oil chamber of the screed lift cylinder 25. As a result, the screed lift cylinder 25 contracts, the rear end portion of the leveling arm 3A is lifted, and the screed 3 is lifted. On the other hand, when the lifted screed 3 is to be lowered, the controller 50 allows the hydraulic oil in the rod side oil chamber of the screed lift cylinder 25 to flow out. As a result, the screed lift cylinder 25 extends due to the weight of the screed 3, and the rear end portion of the leveling arm 3A descends, lowering the screed 3. Hereinafter, the function of lifting the screed 3 using the screed lift cylinder 25 and lowering the lifted screed 3 may be referred to as the "screed lift function".

[0039] The asphalt finisher 100 also includes a side plate 40, an extendable moldboard, a screed step 42, and a retaining plate 43.

[0040] The side plates 40 are attached to the outer end in the vehicle width direction of the telescopic screed 31. The side plates 40 include a left side plate 40L and a right side plate 40R. Specifically, the left side plate 40L is attached to the outer end (left end) in the vehicle width direction (Y-axis direction) of the left telescopic screed 31L, and the right side plate 40R is attached to the outer end (right end) in the vehicle width direction of the right telescopic screed 31R.

[0041] The telescopic moldboard 41 is a member for adjusting the amount of paving material that remains in front of the telescopic screed 31 out of the paving material spread by the screw SC. The telescopic moldboard 41 is configured to be able to expand and contract in the vehicle width direction together with the telescopic screed 31. A side plate 40 is connected to the outer end of the telescopic moldboard 41 in the vehicle width direction (Y-axis direction).

[0042] Specifically, the telescopic moldboard 41 is a plate-like member extending in the vehicle width direction, and includes a left telescopic moldboard 41L and a right telescopic moldboard 41R. A left side plate 40L is attached to the outer end (left end) in the vehicle width direction of the left telescopic moldboard 41L, and a right side plate 40R is attached to the outer end (right end) of the right telescopic moldboard 41R.

[0043] The extendable moldboard 41 is configured to be adjustable in height in the Z-axis direction, independent of the extendable screed 31 and the side plate 40. This allows the asphalt finisher 100 to adjust the size of the gap between the lower end of the extendable moldboard 41 and the roadbed by moving the extendable moldboard 41 up and down, and as a result, adjust the amount of paving material passing through the gap. Therefore, the asphalt finisher 100 can adjust the amount (height) of paving material remaining in the area behind the extendable moldboard 41 and in front of the extendable screed 31 by moving the extendable moldboard 41 up and down. In addition, the asphalt finisher 100 can adjust the amount of paving material taken in below the extendable screed 31.

[0044] The screed step 42 is a member used as a foothold when a worker works behind the screed 3. Specifically, the screed step 42 includes a left screed step 42L, a central screed step 42C, and a right screed step 42R.

[0045] The retaining plate 43 is a plate-shaped member for preventing the paving material sent out in the vehicle width direction by the screw SC from scattering in front of the screw SC. The asphalt finisher 100 can appropriately send out the paving material in the vehicle width direction by using the screw SC due to the action of the retaining plate 43. Specifically, the retaining plate 43 includes a left retaining plate 43L and a right retaining plate 43R.

[0046] [Function configuration] Next, the functional configuration of the controller 50 will be described with reference to Fig. 2 in addition to Fig. 1A and Fig. 1B. Specifically, the functional configuration of the controller 50 related to the adjustment function of the driving force of the front wheels 6 (hereinafter, "front wheel driving force adjustment function") will be described.

[0047] FIG. 2 is a functional block diagram showing an example of the configuration of the controller 50. As shown in FIG.

[0048] The controller 50 includes a pavement material weight acquisition unit 50A and a front wheel driving force control unit 50B. The functions of the pavement material weight acquisition unit 50A and the front wheel driving force control unit 50B are realized, for example, by loading a predetermined program installed in an auxiliary storage device into a memory device and executing the program on a CPU.

[0049] The paving material weight acquisition unit 50A acquires information regarding the weight of the paving material inside the hopper 2. Specifically, the paving material weight acquisition unit 50A may repeat a process of acquiring information regarding the weight of the paving material inside the hopper 2 at each predetermined control period while the asphalt finisher 100 is in operation.

[0050] The paving material weight acquisition unit 50A estimates the amount (volume) of paving material inside the hopper 2, for example, based on output data captured from the spatial recognition device CM. At this time, the paving material weight acquisition unit 50A may estimate the amount (volume) of paving material inside the hopper 2, taking into account the open / closed state of the hopper 2, i.e., the expansion / contraction state of the hopper cylinder 24. This is because the shape of the portion of the hopper 2 that contains the paving material changes depending on the open / closed state of the hopper 2. The paving material weight acquisition unit 50A may then estimate (calculate) the weight of the paving material inside the hopper 2, based on the estimated volume of the paving material inside the hopper 2, the density of the paving material (mass per unit volume), and the like.

[0051] Furthermore, the paving material weight acquisition unit 50A may estimate (calculate) the weight of the paving material inside the hopper 2 based on the output of a load cell or a strain gauge installed in the hopper 2, for example.

[0052] The front wheel driving force control unit 50B (an example of a control unit) performs control to adjust the driving force of the front wheels 6 based on information on the weight of the paving material inside the hopper 2 acquired by the paving material weight acquisition unit 50A. Specifically, the front wheel driving force control unit 50B repeatedly performs processing related to control to adjust the driving force of the front wheels 6 at each predetermined control cycle while synchronizing with the processing of the paving material weight acquisition unit 50A.

[0053] The front wheel driving force control section 50B adjusts the driving force of the front wheels 6 to be relatively large when the weight of the paving material inside the hopper 2 is relatively large. On the other hand, the front wheel driving force control section 50B adjusts the driving force of the front wheels 6 to be relatively small when the weight of the paving material inside the hopper 2 is relatively small. This allows the controller 50 to adjust the driving force of the front wheels 6 in accordance with the weight of the paving material inside the hopper 2, i.e., the load acting on the front wheels 6. This makes it possible to prevent the driving force of the front wheels 6 from exceeding the frictional force between the front wheels 6 and the roadbed, causing the front wheels 6 to slip (wheel spin).

[0054] Specifically, the front wheel driving force control unit 50B controls the driving force of the front wheels 6 so as to maintain a target value that is changed in accordance with changes in the weight of the paving material acquired by the paving material weight acquisition unit 50A while the asphalt finisher 100 (tractor 1) is traveling. This allows the controller 50 to realize a system that corresponds to the weight of the paving material inside the hopper 2.

[0055] The front wheel driving force control section 50B may control (adjust) the driving force of the front wheels 6, for example, by outputting a control command to a relief valve RV described below and adjusting the pressure of hydraulic oil supplied to a front wheel driving motor 22 described below that drives the front wheels 6. In other words, the front wheel driving force control section 50B may realize adjustment of the driving force of the front wheels 6 by directly controlling the relief valve RV.

[0056] Furthermore, the front wheel driving force control section 50B may output a control command to a front wheel driving pump 14F (specifically, a regulator that adjusts the tilt angle of the swash plate of the front wheel driving pump 14F) described below in addition to the relief valve RV. In other words, the front wheel driving force control section 50B may adjust the driving force of the front wheels 6 by directly controlling the front wheel driving pump 14F (regulator) in addition to the relief valve RV. This enables the front wheel driving force control section 50B to adjust the angle of the swash plate of the front wheel driving pump 14F (hereinafter, "tilt angle") and adjust the pressure of the hydraulic oil supplied to the front wheel driving motor 22.

[0057] The front wheel driving force control section 50B may, for example, determine a target value of the driving force of the front wheels 6 in accordance with the weight of the paving material inside the hopper 2, and control the control amount of the directly controlled object (the relief valve RV and the front wheel driving pump 14F) so as to realize the determined target value. The front wheel driving force control section 50B may also control the control amount of the directly controlled object in accordance with a control law (see FIG. 4 described later) that represents the relationship between the weight of the paving material and the control amount of the directly controlled object, which is predefined so as to realize a target value of the driving force of the front wheels 6 in accordance with the weight of the paving material. This allows the controller 50 to control the driving force of the front wheels 6 so as to maintain the target value of the driving force of the front wheels 6, which is changed in accordance with the change in the weight of the paving material inside the hopper 2. Therefore, the controller 50 can appropriately control the driving force of the front wheels 6 in accordance with the change in the weight of the paving material inside the hopper 2.

[0058] [Hydraulic system] Next, with reference to FIG. 3, a hydraulic system mounted on the asphalt finisher 100 will be described.

[0059] FIG. 3 is a hydraulic circuit diagram showing an example of the configuration of a hydraulic system of the asphalt finisher 100.

[0060] The hydraulic system includes a hydraulic source 14, a rear wheel drive unit F1, a conveyor screw drive unit F2, a front wheel drive unit F3, a steering and compaction device drive unit F4, a leveling unit F5, a hopper drive unit F6, a screed lift unit F7, and a screed extension unit F8.

[0061] The hydraulic power source 14 draws up hydraulic oil from a hydraulic oil tank T and supplies the hydraulic oil to various drive parts. The hydraulic power source 14 includes an engine 14E, a rear wheel drive pump 14R, a charge pump 14C, a cylinder pump 14M, a conveyor screw pump 14S, and a front wheel drive pump 14F.

[0062] The engine 14E is a drive source that drives the rear wheel drive pump 14R, the charge pump 14C, the cylinder pump 14M, the conveyor screw pump 14S, and the front wheel drive pump 14F.

[0063] The rear wheel drive pump 14R is a variable displacement hydraulic pump that supplies hydraulic oil for driving the rear wheel drive unit F1. Specifically, the rear wheel drive pump 14R may be a swash plate type variable displacement bidirectional hydraulic pump used in a closed circuit.

[0064] The charge pump 14C is a fixed displacement hydraulic pump that supplies hydraulic oil for control to the rear wheel drive unit F1.

[0065] The cylinder pump 14M is a variable displacement hydraulic pump capable of supplying hydraulic oil to each of the steering / compaction device drive unit F4, the leveling unit F5, the hopper drive unit F6, the screed lift unit F7, and the screed extension / retraction unit F8. The cylinder pump 14M is a swash plate type variable displacement hydraulic pump, and the discharge amount is controlled so that the discharge pressure is constant at a predetermined pressure.

[0066] The conveyor screw pump 14S is a variable displacement hydraulic pump that supplies hydraulic oil to the conveyor screw driving unit F2. Specifically, the conveyor screw pump 14S may be a swash plate type variable displacement hydraulic pump.

[0067] The front wheel drive pump 14F (an example of a hydraulic pump) is a variable displacement hydraulic pump that supplies hydraulic oil to the front wheel drive unit F3. Specifically, the front wheel drive pump 14F is a swash plate type variable displacement hydraulic pump.

[0068] The rear wheel drive unit F1 is configured to be able to drive the rear wheels 5 using hydraulic oil supplied from the hydraulic source 14. The rear wheel drive unit F1 includes a left rear wheel drive motor 20L, a right rear wheel drive motor 20R, check valves 20La, 20Ra, relief valves 20Lb, 20Rb, and a reduction gear switching valve V0.

[0069] The left rear wheel drive motor 20L and the right rear wheel drive motor 20R drive the left and right rear wheels, respectively. Specifically, the left rear wheel drive motor 20L and the right rear wheel drive motor 20R may be infinitely variable speed hydraulic motors and may form a closed circuit, i.e., a hydrostatic transmission (HST) circuit, together with the rear wheel drive pump 14R.

[0070] The check valve 20La maintains the pressure of the hydraulic oil in the pipe C1 connecting the first port ((1) in the figure) of the rear wheel drive pump 14R and the second ports ((2) in the figure) of the left rear wheel drive motor 20L and the right rear wheel drive motor 20R at a predetermined pressure or higher. Specifically, when the pressure of the hydraulic oil in the pipe C1 falls below the discharge pressure of the charge pump 14C, the check valve 20La allows the hydraulic oil discharged by the charge pump 14C to flow into the pipe C1. Similarly, the check valve 20Ra maintains the pressure of the hydraulic oil in the pipe C2 connecting the second port ((2) in the figure) of the rear wheel drive pump 14R and the first ports ((1) in the figure) of the left rear wheel drive motor 20L and the right rear wheel drive motor 20R at a predetermined pressure or higher. Specifically, when the pressure of the hydraulic oil in the pipe C2 falls below the discharge pressure of the charge pump 14C, the check valve 20Ra allows the hydraulic oil discharged by the charge pump 14C to flow into the pipe C2.

[0071] The relief valve 20Lb maintains the pressure of the hydraulic oil in the pipe C1 at or below a predetermined relief pressure. Specifically, when the pressure of the hydraulic oil in the pipe C1 exceeds the relief pressure, the relief valve 20Lb allows the hydraulic oil in the pipe C1 to flow out of the closed circuit (for example, to the hydraulic oil tank T). Similarly, the relief valve 20Rb maintains the pressure of the hydraulic oil in the pipe C2 at or below a predetermined relief pressure. Specifically, when the pressure of the hydraulic oil in the pipe C2 exceeds the relief pressure, the relief valve 20Rb allows the hydraulic oil in the pipe C2 to flow out of the closed circuit (for example, to the hydraulic oil tank T).

[0072] The speed reducer switching valve V0 switches the reduction ratio of each of the left rear wheel driving motor 20L and the right rear wheel driving motor 20R. Specifically, the speed reducer switching valve V0 switches the reduction ratio of each of the left rear wheel driving motor 20L and the right rear wheel driving motor 20R by using the hydraulic oil discharged by the charge pump 14C in response to a control command from the controller 50.

[0073] The conveyor / screw driving unit F2 is configured to be able to drive the conveyor CV and the screw SC using hydraulic oil supplied from the hydraulic source 14. The conveyor / screw driving unit F2 includes a conveyor motor 21C, a screw motor 21S, a conveyor control valve V1C, and a screw control valve V1S.

[0074] The conveyor motor 21C and the screw motor 21S are both variable displacement hydraulic motors that form an open circuit. The conveyor motor 21C includes a left conveyor motor 21CL and a right conveyor motor 21CR. The screw motor 21S includes a left screw motor 21SL and a right screw motor 21SR. The conveyor control valve V1C includes a left conveyor control valve V1CL and a right conveyor control valve V1CR. The screw control valve V1S includes a left screw control valve V1SL and a right screw control valve V1SR.

[0075] The left conveyor control valve V1CL operates in response to a control command from the controller 50, and allows the hydraulic oil discharged by the conveyor screw pump 14S to flow into the suction port of the left conveyor motor 21CL, and allows the hydraulic oil flowing out from the discharge port of the left conveyor motor 21CL to be discharged into the hydraulic oil tank T. The right conveyor control valve V1CR operates in response to a control command from the controller 50, and allows the hydraulic oil discharged by the conveyor screw pump 14S to flow into the suction port of the right conveyor motor 21CR, and allows the hydraulic oil flowing out from the discharge port of the right conveyor motor 21CR to be discharged into the hydraulic oil tank T. Similarly, the left screw control valve V1SL operates in response to a control command from the controller 50, and allows the hydraulic oil discharged by the conveyor screw pump 14S to flow into the suction port of the left screw motor 21SL, and allows the hydraulic oil flowing out from the discharge port of the left screw motor 21SL to be discharged into the hydraulic oil tank T. The right screw control valve V1SR operates in response to a control command from the controller 50 to allow the hydraulic oil discharged by the conveyor / screw pump 14S to flow into the suction port of the right screw motor 21SR, and to discharge the hydraulic oil flowing out from the discharge port of the right screw motor 21SR into the hydraulic oil tank T. The hydraulic oil flowing out from the discharge ports of the left conveyor motor 21CL, the right conveyor motor 21CR, the left screw motor 21SL, and the right screw motor 21SR is discharged into the hydraulic oil tank T through the oil cooler OC.

[0076] The front wheel drive section F3 is configured to be able to drive the front wheels 6 using hydraulic oil supplied from the hydraulic source 14. The front wheel drive section F3 includes a front wheel drive motor 22, a front wheel drive valve V2, and a relief valve RV.

[0077] The front wheel drive motor 22 (an example of a hydraulic motor) is a fixed displacement hydraulic motor that forms an open circuit. The front wheel drive motor 22 includes a left front wheel drive motor 22L that drives the left front wheel 6L (see FIG. 5) of the front wheels 6, and a right front wheel drive motor 22R that drives the right front wheel 6R (see FIG. 5) of the front wheels 6.

[0078] The front wheel running valve V2 operates in response to a control command from the controller 50, and causes the hydraulic oil discharged from the front wheel running pump 14F to flow into the suction port of the front wheel running motor 22. The front wheel running pump 14F supplies hydraulic oil in parallel to each of the left front wheel running motor 22L and the right front wheel running motor 22R via the front wheel running valve V2.

[0079] The relief valve RV is provided in an oil passage between the front wheel driving pump 14F and the front wheel driving valve V2. The relief valve RV is, for example, an electromagnetic relief valve. When the pressure of the hydraulic oil in the oil passage between the front wheel driving pump 14F and the front wheel driving motor 22 reaches a predetermined relief pressure, the relief valve RV discharges the hydraulic oil in the oil passage to the hydraulic oil tank T. This makes it possible to limit the pressure of the hydraulic oil supplied to the front wheel driving motor 22 to a predetermined relief pressure or less.

[0080] The relief pressure of the relief valve RV is variable. Specifically, the controller 50 transmits a control command specifying the setting content (set value) of the relief pressure to the relief valve RV. As a result, the relief valve RV sets (changes) the relief pressure according to the control command input from the controller 50. This allows the relief valve RV to maintain the pressure of the hydraulic oil in the oil passage between the front wheel running pump 14F and the front wheel running motor 22 at or below the set relief pressure. Therefore, the controller 50 (front wheel driving force control section 50B) adjusts the pressure of the hydraulic oil supplied to the front wheel running motor 22 by varying the relief pressure of the relief valve RV, and as a result, can adjust the driving force of the front wheels 6.

[0081] The steering / compaction device drive unit F4 is configured to be able to drive the steering device and the compaction device (neither of which are shown) using hydraulic oil supplied from a hydraulic source 14.

[0082] The steering device is a hydraulic device for steering the front wheels 6. For example, the steering device changes the steering angle of the front wheels 6 by using hydraulic oil discharged from the cylinder pump 14M in response to the operation of the steering wheel by the operator. The compaction device is a hydraulic device for compacting the paving material. The compaction device includes a tamper and a vibrator, and operates the tamper and vibrator by using hydraulic oil discharged from the cylinder pump 14M.

[0083] The leveling unit F5 is configured to be able to adjust the paving thickness using hydraulic oil supplied from the hydraulic source 14. The leveling unit F5 includes a leveling cylinder 23, a leveling control valve 33, and a pilot check valve 33P.

[0084] As described above, the leveling cylinder 23 moves the leveling arm 3A up and down to adjust the paving thickness. Specifically, the leveling cylinder 23 is configured to contract when increasing the paving thickness and to extend when decreasing the paving thickness. The leveling cylinder 23 includes a left leveling cylinder 23L and a right leveling cylinder 23R.

[0085] The leveling control valve 33 operates in response to a control signal from the controller 50 to control the flow rate and flow direction of the hydraulic oil supplied to the leveling cylinder 23. The leveling control valve 33 includes a left leveling control valve 33L and a right leveling control valve 33R. When increasing the pavement thickness, the left leveling control valve 33L causes the hydraulic oil discharged by the cylinder pump 14M to flow into the rod side oil chamber of the left leveling cylinder 23L, and causes the hydraulic oil flowing out of the head side oil chamber of the left leveling cylinder 23L to be discharged into the hydraulic oil tank T. In this case, the left leveling cylinder 23L contracts, and the left leveling arm 3AL rises. The same applies to the right leveling control valve 33R that contracts the right leveling cylinder 23R. On the other hand, when reducing the pavement thickness, the left leveling control valve 33L causes the hydraulic oil discharged by the cylinder pump 14M to flow into the head side oil chamber of the left leveling cylinder 23L, and causes the hydraulic oil flowing out of the rod side oil chamber of the left leveling cylinder 23L to be discharged into the hydraulic oil tank T. In this case, the left leveling cylinder 23L extends, and the left leveling arm 3AL descends. The same is true for the right leveling control valve 33R that extends the right leveling cylinder 23R.

[0086] The pilot check valve 33P is configured to prevent the leveling cylinder 23 from moving due to an external force. The pilot check valve 33P includes pilot check valves 33PaL, 33PbL, 33PaR, and 33PbR. For example, the pilot check valve 33PaL allows the hydraulic oil in the rod side oil chamber of the left leveling cylinder 23L to flow toward the hydraulic oil tank T only when the left leveling control valve 33L operates in response to an operator's operation and the hydraulic oil discharged by the cylinder pump 14M flows into the head side oil chamber of the left leveling cylinder 23L. The pilot check valve 33PaL prohibits the hydraulic oil in the rod side oil chamber of the left leveling cylinder 23L from flowing toward the hydraulic oil tank T in other cases. The same applies to the pilot check valves 33PbL, 33PaR, and 33PbR.

[0087] The hopper driving unit F6 is configured to be able to open and close the hopper 2 using hydraulic oil supplied from the hydraulic source 14. The hopper driving unit F6 includes a hopper cylinder 24, a hopper control valve 34, and a pilot check valve 34P.

[0088] The hopper cylinder 24 opens and closes the hopper 2. The hopper cylinder 24 contracts when opening the hopper 2, and expands when closing the hopper 2. The hopper cylinder 24 includes a left hopper cylinder 24L and a right hopper cylinder 24R.

[0089] The hopper control valve 34 operates in response to a control signal from the controller 50 to control the flow rate and flow direction of the hydraulic oil supplied to the hopper cylinder 24. The hopper control valve 34 includes a left hopper control valve 34L and a right hopper control valve 34R. When opening the hopper 2, the left hopper control valve 34L allows the hydraulic oil discharged by the cylinder pump 14M to flow into the rod side oil chamber of the left hopper cylinder 24L, and discharges the hydraulic oil flowing out of the head side oil chamber of the left hopper cylinder 24L to the hydraulic oil tank T. In this case, the left hopper cylinder 24L contracts. In addition, the right hopper control valve 34R allows the hydraulic oil discharged by the cylinder pump 14M to flow into the rod side oil chamber of the right hopper cylinder 24R, and discharges the hydraulic oil flowing out of the head side oil chamber of the right hopper cylinder 24R to the hydraulic oil tank T. In this case, the right hopper cylinder 24R contracts. On the other hand, when the hopper 2 is closed, the left hopper control valve 34L allows the hydraulic oil discharged by the cylinder pump 14M to flow into the head side oil chamber of the left hopper cylinder 24L, and discharges the hydraulic oil flowing out of the rod side oil chamber of the left hopper cylinder 24L to the hydraulic oil tank T. In this case, the left hopper cylinder 24L extends. In addition, the right hopper control valve 34R allows the hydraulic oil discharged by the cylinder pump 14M to flow into the head side oil chamber of the right hopper cylinder 24R, and discharges the hydraulic oil flowing out of the rod side oil chamber of the right hopper cylinder 24R to the hydraulic oil tank T. In this case, the right hopper cylinder 24R extends.

[0090] The pilot check valve 34P is configured to prevent the hopper cylinder 24 from contracting due to the weight of the hopper 2 or the weight of the hopper 2 and the paving material in the hopper 2, causing the hopper 2 to open. The pilot check valve 34P includes a pilot check valve 34PL and a pilot check valve 34PR. For example, the pilot check valve 34PL allows the hydraulic oil in the head side oil chamber of the left hopper cylinder 24L to flow toward the hydraulic oil tank T only when the left hopper control valve 34L operates in response to the operation of the operator and the hydraulic oil discharged by the cylinder pump 14M flows into the rod side oil chamber of the left hopper cylinder 24L. The pilot check valve 34PL prohibits the hydraulic oil in the head side oil chamber of the left hopper cylinder 24L from flowing toward the hydraulic oil tank T in other cases. The same applies to the pilot check valve 34PR.

[0091] In the hopper drive unit F6, a pilot check valve is not provided between the rod side oil chamber of the hopper cylinder 24 and the hopper control valve 34. This is because the weight of the hopper 2 is large, so there is a low possibility that the hopper cylinder 24 will be unintentionally extended by an external force. However, a pilot check valve may be provided between the rod side oil chamber of the hopper cylinder 24 and the hopper control valve 34.

[0092] The screed lift section F7 is configured to be able to lift the screed 3 and lower the lifted screed using hydraulic oil supplied from the hydraulic source 14. The screed lift section F7 includes a screed lift cylinder 25, a screed lift control valve 35, a changeover valve 35a, a relief valve 35b, and a changeover valve 35c.

[0093] As described above, the screed lift cylinders 25 lift the screed 3 and lower the lifted screed 3. Specifically, the screed lift cylinders 25 contract when lifting the screed 3 and extend when lowering the screed 3. The screed lift cylinders 25 include a left screed lift cylinder 25L and a right screed lift cylinder 25R.

[0094] The screed lift control valve 35 operates in response to a control signal from the controller 50 to control the flow rate and flow direction of the hydraulic oil supplied to the screed lift cylinder 25. When the screed 3 is lifted, the screed lift control valve 35 causes the hydraulic oil discharged by the cylinder pump 14M to flow into the rod side oil chamber of the screed lift cylinder 25. In this case, the changeover valve 35a is switched to a first position including a check valve in response to a control signal from the controller 50. This makes it possible to prevent the hydraulic oil from flowing back from the rod side oil chamber of the screed lift cylinder 25 toward the hydraulic oil tank T. The hydraulic oil flowing out of the head side oil chamber of the screed lift cylinder 25 is discharged into the hydraulic oil tank T without passing through the screed lift control valve 35. In this case, the screed lift cylinder 25 contracts. On the other hand, when the screed 3 is lowered to the ground, the screed lift control valve 35 is not used and is maintained in the state shown in FIG. 3. In this case, the changeover valve 35a is switched to a second position including no check valve in response to a control signal from the controller 50. This allows the hydraulic oil in the rod side oil chamber of the screed lift cylinder 25 to flow out toward the hydraulic oil tank T. Therefore, the screed lift cylinder 25 extends due to the weight of the screed 3, and the hydraulic oil in the rod side oil chamber of the screed lift cylinder 25 is discharged into the hydraulic oil tank T through the switching valve 35a and the relief valve 35b.

[0095] The changeover valve 35a and the relief valve 35b realize the up and down movement of the screed 3 in accordance with the change in the lifting force (i.e., the force of the paving material trying to lift the screed 3) generated when the asphalt finisher 100 moves and paves the road. Specifically, when the screed 3 rises due to an increase in the lifting force, the screed lift cylinder 25 contracts. In this case, the hydraulic oil discharged from the cylinder pump 14M flows into the rod side oil chamber of the screed lift cylinder 25 through the pipe C3, the screed lift control valve 35, and the changeover valve 35a. On the other hand, when the screed 3 descends due to a decrease in the lifting force, the screed lift cylinder 25 extends. In this case, the hydraulic oil flowing out from the rod side oil chamber of the screed lift cylinder 25 is discharged into the hydraulic oil tank T through the changeover valve 35a, the screed lift control valve 35, and the relief valve 35b. The changeover valve 35c is switched to a first position including a check valve in response to a control signal from the controller 50 when the asphalt finisher 100 is moving and paving the road, i.e., while the downstream hydraulic devices such as the screed extension / retraction part F8 are not being used. This makes it possible to prevent adverse effects on the downstream hydraulic devices such as the screed extension / retraction part F8. Specifically, this is to prevent the extension / retraction screed 31, the crown device, the step device (none of which are shown) and the like from moving unintentionally.

[0096] The screed extension / retraction section F8 is configured to be able to extend and retract the extendable screed 31 in the vehicle width direction (Y-axis direction) using hydraulic oil supplied from the hydraulic source 14. The screed extension / retraction section F8 includes a screed extension / retraction cylinder 27, a screed extension / retraction control valve 37, a pilot check valve 37P, and a relief valve 37V.

[0097] The screed extension / retraction control valve 37 operates in response to a control signal from the controller 50 to control the flow rate and flow direction of the hydraulic oil supplied to the screed extension / retraction cylinder 27. The screed extension / retraction control valve 37 includes a left screed extension / retraction control valve 37L and a right screed extension / retraction control valve 37R.

[0098] When the left telescopic screed 31L is retracted, the left screed extension control valve 37L allows the hydraulic oil discharged by the cylinder pump 14M to flow into the rod side oil chamber of the left screed telescopic cylinder 27L, and allows the hydraulic oil flowing out of the head side oil chamber of the left screed telescopic cylinder 27L to be discharged into the hydraulic oil tank T. In this case, the left screed telescopic cylinder 27L is contracted, and the left telescopic screed 31L is retracted. The same is true when the right screed 31R is retracted by the right screed extension control valve 37R. On the other hand, when the left telescopic screed 31L is pushed out, the left screed extension control valve 37L allows the hydraulic oil discharged by the cylinder pump 14M to flow into the head side oil chamber of the left screed telescopic cylinder 27L, and allows the hydraulic oil flowing out of the rod side oil chamber of the left screed telescopic cylinder 27L to be discharged into the hydraulic oil tank T. In this case, the left screed telescopic cylinder 27L extends and the left telescopic screed 31L is pushed out. The same applies to the case where the right screed 31R is retracted by the right screed telescopic control valve 37R.

[0099] The pilot check valve 37P is configured to prevent unintentional movement of the screed telescopic cylinder 27 due to an external force. The pilot check valve 37P includes pilot check valves 37PaL, 37PaR, 37PbL, and 37PbR.

[0100] For example, the pilot check valve 37PaL allows hydraulic oil in the rod side oil chamber of the left screed telescopic cylinder 27L to flow toward the hydraulic oil tank T only when the left screed telescopic control valve 37L operates in response to operation by the operator and hydraulic oil discharged by the cylinder pump 14M flows into the head side oil chamber of the left screed telescopic cylinder 27L. The pilot check valve 37PaL prohibits hydraulic oil in the rod side oil chamber of the left screed telescopic cylinder 27L from flowing toward the hydraulic oil tank T in all other cases. The same is true for the pilot check valves 37PbL, 37PaR, 37PbR.

[0101] The relief valves 37V are configured to prevent members associated with the telescopic screed 31 from being destroyed by excessive external force acting in a direction to retract the telescopic screed 31. The relief valves 37V include a left relief valve 37VL and a right relief valve 37VR.

[0102] For example, when the left screed telescopic cylinder 27L receives an excessive external force acting in a direction to retract the left screed telescopic cylinder 27L and the pressure of the hydraulic oil in the head-side oil chamber of the left screed telescopic cylinder 27L rises excessively, the left relief valve 37VL allows the hydraulic oil in the head-side oil chamber to flow out to the hydraulic oil tank T. As a result, the left screed telescopic cylinder 27L retracts to absorb part of the external force and prevent damage to the left telescopic screed 31L. The same applies to the right relief valve 37VR.

[0103] [Specific example of how to adjust the driving force of the front wheels] Next, a method for adjusting the driving force of the front wheels 6 by the controller 50 will be specifically described with reference to FIGS. 4 and 5 in addition to FIGS.

[0104] FIG. 4 is a diagram for explaining an example of a method for controlling the driving force of the front wheels 6. Specifically, FIG. 4 includes a control law 400 showing the relationship between the weight of the paving material inside the hopper 2 and the relief pressure (set value) of the relief valve RV set by the controller 50. FIGS. 5A to 5D are front views showing the state of the paving material PM inside the hopper 2. Specifically, FIG. 5A shows the state of the paving material PM inside the hopper 2 immediately after the paving material PM is supplied by a dump truck. FIG. 5B shows the state of the paving material PM inside the hopper 2 when the amount has decreased compared to the state of FIG. 5A. FIG. 5C shows the state of the paving material PM inside the hopper 2 when the hopper 2 is closed to a certain extent (specifically, about halfway) due to a relative decrease in the amount of paving material PM inside the hopper 2. FIG. 5D shows the amount of paving material PM inside the hopper 2 when the amount of paving material PM inside the hopper 2 has further decreased from the state of FIG. 5C and the hopper 2 is completely closed.

[0105] In Fig. 5, the paving material PM inside the hopper 2 is hatched with matte finish. In Fig. 5A, the base part 1BF, front wheels 6 (left front wheel 6L and right front wheel 6R), and hopper cylinder 24 (left hopper cylinder 24L and right hopper cylinder 24R) of the tractor 1 are shown, but these are omitted in Fig. 5B to Fig. 5D. In Fig. 5A, Fig. 5C, and Fig. 5D, the part of the entrance OP of the conveying passage CP provided on the front surface 1FW of the tractor 1 that is buried in the paving material PM and cannot be seen directly from the front (i.e., is not exposed) is shown by a dashed line.

[0106] As shown in FIGS. 5A to 5D, the paving material PM is stored inside the hopper 2, specifically, in a space surrounded by the front surface 1FW of the tractor 1 and the left and right hopper wings 2W (the left hopper wing 2WL and the right hopper wing 2WR).

[0107] As shown in FIG. 5A, a sufficient amount of paving material PM is accumulated inside the hopper 2 immediately after the paving material PM is supplied from the dump truck. In contrast, as shown in FIG. 5B to FIG. 5D, the amount of paving material PM inside the hopper 2 decreases as the construction of asphalt pavement by the asphalt finisher 100 progresses. At this time, as shown in FIG. 5B, the paving material PM decreases from the center of the inside of the hopper 2 where the conveyor CV is provided. Therefore, as shown in FIG. 5C and FIG. 5D, when the amount of paving material inside the hopper 2 decreases to a certain extent, the hopper 2 is closed, and the paving material PM at both the left and right ends inside the hopper 2 is collected in the center. This makes it possible to prevent the paving material PM from remaining at the left and right ends inside the hopper 2.

[0108] As described above, the hopper 2 may be closed by the operation of an operator monitoring the state inside the hopper 2. The hopper 2 may also be closed automatically, without the operation of an operator. In this case, the controller 50 may determine whether or not the closing operation of the hopper 2 is required, depending on the amount (estimated value) of paving material inside the hopper 2, which is estimated based on the output of the spatial recognition device CM. The controller 50 may also determine the amount (angle) of closure of the hopper 2 based on the amount (estimated value) of paving material. The controller 50 may then control the hopper drive unit F6 (hopper control valve 34) so ​​that the amount of extension and contraction of the hopper cylinder 24 becomes the determined amount of closure of the hopper 2.

[0109] Here, when the driving force of the front wheels 6 is maintained at a relatively high state and the construction work of asphalt paving by the asphalt finisher 100 progresses to a certain extent, the driving force of the front wheels 6 may become larger than the maximum friction force between the front wheels 6 and the roadbed. This is because the load on the front wheels 6 decreases due to a decrease in the amount of paving material PM inside the hopper 2 as the construction work progresses. As a result, there is a possibility that the front wheels 6 may slip (wheel spin), damaging the roadbed or reducing the propulsive force of the asphalt finisher 100.

[0110] In contrast, in this embodiment, the controller 50 (front wheel driving force control unit 50B) adjusts the driving force of the front wheels 6 according to the amount of paving material inside the hopper 2. Specifically, the front wheel driving force control unit 50B adjusts the driving force of the front wheels 6 so that the driving force of the front wheels 6 decreases as the amount of paving material inside the hopper 2 decreases. In this way, the controller 50 can prevent a situation in which the driving force of the front wheels 6 becomes excessively larger than the maximum frictional force of the front wheels 6 when the weight of the paving material inside the hopper 2 decreases relatively. Therefore, in this embodiment, the controller 50 can prevent damage to the roadbed and a decrease in the propulsion force of the asphalt finisher 100 caused by slipping of the front wheels 6.

[0111] 4, the controller 50 may control the relief pressure (set value) of the relief valve RV in accordance with the control law 400 so that the relief pressure of the relief valve RV decreases as the weight of the paving material inside the hopper 2 decreases. As a result, the pressure (maximum value) of the hydraulic oil supplied to the front wheel driving motor 22 through the oil passage between the front wheel driving pump 14F and the front wheel driving motor 22 decreases as the weight of the paving material inside the hopper 2 decreases. Therefore, the controller 50 can specifically reduce the driving force of the front wheels 6 in accordance with the decrease in the amount of paving material inside the hopper 2.

[0112] As described above, the controller 50 may adjust the driving force of the front wheels 6 by controlling the tilt angle of the swash plate of the front wheel driving pump 14F, in addition to controlling the relief pressure of the relief valve RV.

[0113] Furthermore, as described above, the controller 50 may specifically set a target value for the driving force of the front wheels 6 in accordance with the weight of the paving material inside the hopper 2, and adjust the control amount of the relief valve RV and the front wheel driving pump 14F (regulator) so as to realize the target value. In this case, a control law representing the relationship between the driving force (target value) of the front wheels 6 and the control amount (relief pressure and tilt angle) may be specified in advance.

[0114] [Effect] Next, the operation of the asphalt finisher 100 according to this embodiment will be described.

[0115] In this embodiment, the asphalt finisher 100 is equipped with a controller 50 (front wheel driving force control unit 50B) that controls the driving force of the front wheels 6 of the tractor 1 based on the weight of the paving material in the hopper 2. Specifically, the front wheel driving force control unit 50B changes the driving force of the front wheels 6 of the tractor 1 in accordance with changes in the weight of the paving material inside the hopper 2.

[0116] This allows the asphalt finisher 100 (controller 50) to adjust the driving force of the front wheels 6 in accordance with the decrease in the amount of paving material inside the hopper 2 as the asphalt paving work progresses. Therefore, the asphalt finisher 100 can appropriately reduce the driving force of the front wheels 6 in accordance with the decrease in the load on the front wheels 6 that accompanies the decrease in the amount of paving material inside the hopper 2, thereby suppressing slippage of the front wheels 6. Therefore, the asphalt finisher 100 can suppress damage to the roadbed due to slippage of the front wheels 6.

[0117] Furthermore, in this embodiment, the front wheel driving force control section 50B may reduce the driving force of the front wheels 6 when the weight of the paving material inside the hopper 2 decreases.

[0118] As a result, the asphalt finisher 100 (controller 50) reduces the driving force of the front wheels 6 in accordance with the reduction in the weight of the paving material inside the hopper 2, i.e., the reduction in the load on the front wheels 6, and specifically, can suppress slippage of the front wheels 6.

[0119] In addition, in this embodiment, the front wheel driving force control unit 50B may control the driving force of the front wheels 6 so as to maintain a target value that is changed in accordance with changes in the weight of the paving material inside the hopper 2 while the tractor 1 is traveling.

[0120] This allows the asphalt finisher 100 (controller 50) to appropriately adjust the driving force of the front wheels 6 in accordance with changes in the weight of the paving material inside the hopper 2.

[0121] In this embodiment, the front wheel driving force control section 50B may adjust the relief pressure of the relief valve RV to control the driving force of the front wheels 6. In this embodiment, the front wheel driving force control section 50B may adjust the angle (tilt angle) of the swash plate of the front wheel running pump 14F to control the driving force of the front wheels 6.

[0122] As a result, the asphalt finisher 100 (controller 50) can specifically adjust the driving force of the front wheels 6 by controlling control variables such as the relief pressure of the relief valve RV and the tilt angle of the swash plate of the front wheel driving pump 14F.

[0123] Although the embodiments have been described in detail above, the present disclosure is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist described in the claims.

[0124] Finally, this application claims priority based on Japanese Patent Application No. 2021-057823, filed on March 30, 2021, the entire contents of which are incorporated by reference into this application. [Explanation of symbols]

[0125] 1 Tractor 2 Hopper 2W Hopper Wing 2WL Left Hopper Wing 2WR Right Hopper Wing 3. Screed 3A Leveling Arm 5 Rear wheel 6 Front wheel 14 Hydraulic source 14C Charge Pump 14E Engine 14F Front wheel drive pump (hydraulic pump) 14M Cylinder Pump 14R Rear wheel drive pump 14S Conveyor screw pump 20L Left rear wheel drive motor 20La Check valve 20Lb relief valve 20R Right rear wheel drive motor 20Ra Check valve 20Rb Relief valve 21 Conveyor screw motor 21CL Left conveyor motor 21CR Right conveyor motor 21SL Left screw motor 21SR ​​Right screw motor 22 Front wheel drive motor (hydraulic motor) 23 Leveling cylinder 23L Left leveling cylinder 23R Right leveling cylinder 24 Hopper cylinder 24L Left hopper cylinder 24R Right hopper cylinder 25 Screed Lift Cylinder 25L Left screed lift cylinder 25R Right screed lift cylinder 27 Screed telescopic cylinder 27L Left screed telescopic cylinder 27R Right screed telescopic cylinder 30 Main screed 31 Extendable screed 33 Leveling control valve 33L Left leveling control valve 33R Right leveling control valve 33P, 33PaL, 33PaR, 33PbL, 33PbR Pilot check valve 34 Hopper control valve 34L Left hopper control valve 34R Right hopper control valve 34P, 34PL, 34PR Pilot check valve 35 Screed lift control valve 35a Switching valve 35b Relief valve 35c Switching valve 37 Screed extension control valve 37P, 37PaL, 37PaR, 37PbL, 37PbR Pilot check valve 37V Relief valve 37VL Left relief valve 37VR Right relief valve 40 Side Plate 41 Expandable moldboard 42 Screed Step 43 Retaining plate 50 Controller 50A Pavement material weight acquisition section 50B Front wheel drive force control section (control section) 100 Asphalt finisher CM spatial recognition device CP Transport Passage CV Conveyor F1 rear wheel drive F2 Conveyor screw drive unit F3 front wheel drive F4 Steering and compaction device drive unit F5 Leveling Part F6 Hopper drive unit F7 Screed Lift Unit F8 Screed extension section OC Oil Cooler OP Entrance RV Relief Valve SC screw SCLE Left extension screw SCLM Left main screw SCRE Right extension screw SCRM Right main screw V0 Gear changeover valve V1C Conveyor control valve V1CL Left conveyor control valve V1CR Right conveyor control valve V1S Screw control valve V1SL Left screw control valve V1SR Right screw control valve V2 Front wheel drive valve

Claims

1. A tractor, A hopper installed in front of the tractor to receive paving materials; a conveyor that conveys the paving material in the hopper to the rear side of the tractor; A screw that spreads the paving material transported by the conveyor behind the tractor; A screed that spreads the paving material spread by the screw on the rear side of the screw; a control unit that controls a driving force of a front wheel of the tractor based on a weight of the paving material in the hopper; An estimation unit that estimates the weight; A space recognition device that acquires data for monitoring the condition of the paving material in the hopper; The estimation unit estimates the weight based on an output of the spatial recognition device, The control unit controls a driving force of a front wheel of the tractor based on a result of the weight estimation by the estimation unit. Asphalt finisher.

2. The control unit changes the driving force of the front wheels of the tractor in accordance with the change in weight. An asphalt finisher as claimed in claim 1.

3. The control unit controls the driving force of the front wheels so as to maintain a target value that is changed in accordance with the change in weight while the tractor is traveling. An asphalt finisher as claimed in claim 2.

4. The control unit reduces a driving force of the front wheels when the weight decreases. An asphalt finisher according to claim 2 or 3.

5. A hydraulic motor that drives the front wheels; a hydraulic pump for supplying hydraulic oil to the hydraulic motor; a relief valve provided in an oil passage between the hydraulic pump and the hydraulic motor, The control unit controls the driving force of the front wheels by adjusting the relief pressure of the relief valve. An asphalt finisher according to any one of claims 1 to 4.

6. The control unit controls the driving force of the front wheels by adjusting an angle of a swash plate of the hydraulic pump. An asphalt finisher as claimed in claim 5.

7. The control unit adjusts the relief pressure of the relief valve according to a control law that represents a relationship between the weight and the relief pressure, the control law being defined such that the smaller the weight, the smaller the relief pressure. An asphalt finisher according to claim 5 or 6.

8. the control unit sets a target value of the driving force of the front wheels in accordance with a control law expressing a relationship between the weight and the target value of the driving force of the front wheels, the target value being specified so that the smaller the weight is, the smaller the target value of the driving force of the front wheels is, and adjusts the relief pressure of the relief valve so as to realize the target value of the driving force of the front wheels in accordance with a control law expressing a relationship between the target value of the driving force of the front wheels and the relief pressure. An asphalt finisher according to claim 5 or 6.

9. Based on the output of the spatial recognition device, estimating the volume of the paving material in the hopper while taking into account the open / closed state of the hopper, and estimating the weight based on the estimated volume. An asphalt finisher as claimed in any one of claims 1 to 8.

10. Based on the output of the spatial recognition device, a volume of the paving material in the hopper is estimated, and the hopper is automatically closed based on the estimated volume. An asphalt finisher as claimed in any one of claims 1 to 9.

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